First, 29 bipolar patients provided blood samples and rated their mood. Mood ratings were high for 13 patients, low for 13 other patients, and intermediate for the last three patients.

By analyzing those blood samples, the researchers came up with a list of genes that were more or less active in patients with high and low moods.

Next, the scientists winnowed down the gene list, based on lab tests in mice and brain tissue from people who had died with bipolar disorder, depression, and other mood disorders.

Based on all that work, the scientists identified 10 biomarkers -- five linked to high mood and five tied to low mood -- in bipolar patients.

Lastly, Niculescu's team measured those biomarkers in 19 other bipolar patients and 30 patients with psychotic disorders. The biomarkers weren't perfect at identifying patients with high and low mood, but they were right 60% to 70% of the time.